Process for manufacturing a gallium phosphide electroluminescent device

Abstract

When gallium phosphide is etched with hot phosphoric acid from the surface of a crystal having a (1 1 1) plane, the etched surface becomes a flat and smooth plane inclined at an angle of 45° to 55° to the (1 1 1) plane. Accordingly, when an electroluminescent diode is manufactured by forming a p-n junction on a gallium phosphide crystal having a (1 1 1) plane and etching the crystal with a hot concentrated phosphoric acid etching solution to form a mesa structure, the side faces of the resulting crystal becomes inclined to the plane of the junction at an angle of nearly 45° so that the visible rays generated in the p-n junction are totally reflected on the side faces, thus markedly increasing the intensity of emitted rays in the direction of the optical axis perpendicular to the principal plane of the p-n junction.

What is claimed is: 
     
       1. A method for manufacturing a gallium phosphide electroluminescent device, characterized by providing an anticorrosive polygonal plane mask on the surface of a gallium phosphide crystal containing (1 1 1) planes, and etching the crystal from exposed areas with an aqueous solution consisting essentially of hot concentrated phosphoric acid to form a mesa structure in the form of a truncated polyhedral pyramid. 
     
     
       2. A method according to claim 1, wherein the concentrated phosphoric acid solution contains 70% or more of phosphoric acid. 
     
     
       3. A method according to claim 1, wherein the concentrated phosphoric acid solution is maintained at a temperature in the range of 130° to 220° C, preferably 150° to 180° C. 
     
     
       4. A method according to claim 1, wherein the anticorrosive mask is a metallic film consisting mainly of gold, which is in ohmic contact with the gallium phosphide crystal. 
     
     
       5. A method of manufacturing a gallium phosphide electroluminescent device comprising the steps of forming an epitaxial layer of gallium phosphide having a given conductivity type on the surface of a gallium phosphide wafer having a (1 1 1) plane,   diffusing an impurity into the surface of said epitaxial layer remote from said gallium phosphide wafer to form a region therein having a conductivity type opposite to that of said epitaxial layer,   depositing a conductive film on selected portions of said opposite conductivity type region in ohmic contact therewith to form a rectangular mask defining unmasked exposed regions, and   etching said opposite conductivity type region and epitaxial layer at said exposed region with an aqueous solution consisting essentially of phosphoric acid to form a mesa structure in the form of a truncated polyhedral pyramid, the inclined side faces of said pyramid forming flat and smooth planes inclined at an angle of 45° to 55° to said (1 1 1) plane.   
     
     
       6. A method according to claim 5, wherein said aqueous solution contains at least 70% phosphoric acid and its temperature is in the range 130° to 220° C. 
     
     
       7. A method according to claim 6, wherein said aqueous solution contains approximately 90% phosphoric acid and its temperature is in the range 150° to 180° C.